Copy of Basic Map Reading

8/17/2019 Copy of Basic Map Reading

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Map Reading


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A Map is a birds eye view of thesurrounding area to help guide us

from one place to another.

What is a Map?

A traveller needs a map to help

them find their way aroundmore easily.


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Lines of Longitude

Lines of Longitude run parallel to the Prime

Meridian at Greenwich.

A line of

Longitude is

also referred toas a Meridian


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Lines of Latitude

• Lines of Latitude run parallel to the Equator


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Recording your Position

Lines of Latitude &Longitude cometogether to form amatrix

1.5


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Recording your Position

l First we state its

Latitude followed

by its Longitude

in degrees &

minutes

e.g.:A= 20’N 56’W

B= 17’S 17’W

C= 45’N 15’E

1.5


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Although this system can give reasonably

accurate positioning it is not accurate

enough for everyday use.

So each degree is further broken down

into 60 minutes.


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Topographical Maps

This means they show the shape and surface

detail of the land. This includes natural and

man-made features.


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Looking after your map

Some maps are now produced laminated and you

can treat maps with a waterproof coating

Always keep your map folded

NEVER mark a map surface with ink

If you do need to mark your map do so lightly

with a pencil

Try to avoid getting it wet

If you do get it wet allow it to dry naturally.


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Folding your map

First fold your map in half length wise, with theprinted map outwards like so:


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Then concertinawise:

The unit of height used on this map is in

METRES.


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Latitude / Longitude

The lines of latitude are expressed in degrees

and minutes and are marked along the right

and left (east and west) hand side of the map.

The lines of longitude are marked along the

top and bottom (north and south). The lines

of latitude and longitude are not actuallydrawn on the map itself - it would be too

confusing.


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North

1. True North

2. Grid North

3. Magnetic north

In map reading there are always references to

north. There are in fact 3 north's:


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True North

This is the geographical north pole of the

earth - the point where the earth’s axis meet

the surface.


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Grid North

This north takes its name from the National GridSystem. This is a system of imaginary linesdrawn vertically & horizontally on the mapwhich divide it into a series of squares.

Because Grid lines are drawn on a flat

map and lines of latitude & longitude are

curved like the earth's surface. The 2

systems are different.

This difference is shown on the map (key

position 10) as a difference between True

& Grid north.


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Magnetic North

This is the point the magnetic needle aligns

itself to when freely suspended. The earth hasits own magnetic field.

Unfortunately the earth’s north and southpoles do not line up with the geographical poles

- in fact they are about 1200 miles apart!!


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Sometimes the same symbol is shown in

different colours to signify a difference

Example

Red National Trust symbols show the area is

open all year.

The same symbol in blue indicates it has a

restricted opening period.


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Contour Lines

A contour line is a reddish brown line drawn

on the map joining all points of equal height

above mean sea level (MSL) Mean sea level

is a fixed height approximately half waybetween high and low tides.

By joining all the pointsat the same height you

can achieve a picture

and shape of the land.

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These contour lines will wonder all over the

map and will eventually rejoin at the startpoint to show an area of equal height.

The only exception to this rule is where acontour line meets a cliff face.


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The height is shown in small breaks in the

contour line.

Every 5th line is shown thicker to make themeasier to read.

These contour lines are situated at 10 metre

intervals.The rise & fall between contours is the Vertical

Interval (VI)


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Scales

The objective of this lecture is foryou to be able to display an

reasonable understanding of size and

scale in map work.


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IntroductionIf your map is to cover a reasonable area

then everything on the map has to be

reduced considerably from its real size.


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Why do we use scale?

We use scale so that we can cover a

reasonable area of the ground aroundus and show it on the map.


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How do you express scale?

There are 3 ways to express

scale.

These are:


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A: In Words

B by saying “so many centimetres to the kilometre”

Example: a scale of “2cm to 1km” means

that for every 2 cm on the map you would

travel 1 km on the ground.


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B: As a Representative Fraction

In this method the scale is expressed in the

form of a fraction.

e.g. 1

50,000

Using this method you are saying that anydistances measured on the map are one-

fiftythousanth of the real distance on the

ground.


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A Representative Fraction is

also referred to as RF


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C: As a Ratio

This is very similar to B, but is written as:

1:50,000

this means the same as:

1

50,000


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Calculation

In the case of RF and ratio the expression of

distance, whether it’s inches, centimetres or

metres, is the measurement on the ground

l 1 inch on the map = 50,000 inches on the ground

l 1 cm on the map = 50,000 cm on the ground

l 1 m on the map = 50,000 m on the ground

So a 1:50,000 ratio would be equally validfor:


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If the scale is expressed in words it

may be necessary to convert it intoeither a RF or a ratio.


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For example: to convert a scale of 1 inch to

1 mile, you have to calculate the number ofinches in a mile:

• There are 1,760 yards in a mile

• There are 5,280 feet in a mile (1760 x 3)

• There are 63,360 inches in a mile (5280 x

12)


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So the scale of 1 inch to 1 milecan be expressed as a ratio of

1:63,360.

This type of calculation is made

easier using the metric system,

but it will still require carefulthought.


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Area

When using scales, areas of ground

will also be proportionately reduced

but remember that areas contract

rapidly on small scale maps.


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For example if you take a map that is half the

scale of another, then the area is reduced by

a quarter (not a half). This is because thearea of a rectangular figure is length

multiplied by breadth. If you therefore halved

the scale you will quarter the area of themap.4

4

4 x 4 = 16

2

2

2 x 2 = 4

e.g.


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The same area of ground in three different scales

(Half the scale = One quarter of the area)

1 km square

at 1:12,500

1 km squareat 1:25,000

1 km square

at 1:50,000


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Examples of different scales:

Large scale - City or town maps(defined buildings)

Medium scale - Larger areas (buildings

as symbols)

Small scale - Atlas (large towns inname only)

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Copy of Basic Map Reading